Webster's Dictionary 
(1): ( n.) The act of symbolizing, or the state of being symbolized; as, symbolism in Christian art is the representation of truth, virtues, vices, etc., by emblematic colors, signs, and forms.
(2): ( n.) A system of symbols or representations.
(3): ( n.) A combining together of parts or ingredients.
(4): ( n.) The science of creeds; symbolics.
(5): ( n.) The practice of using symbols, or the system of notation developed thereby.
Cyclopedia of Biblical, Theological and Ecclesiastical Literature 
is that system which represents moral or intellectual qualities by external signs or symbols. It is characteristic of the earlier and ruder stages of development, when the mind and moral nature have not yet grown to the age, which takes direct cognizance of mental and moral qualities, or takes cognizance of them only through external signs that bear a real or a conventional resemblance to them. The Old Test. is full of symbolism; the Jewish Temple, like the Tabernacle which it superseded, though no image of the Deity was permitted in it, was itself a symbol of the soul of man, in which God abides, if it be holy and ready to receive him; and all its utensils, as well as all its services, were symbolical. (See Type), and the various articles on the Old-Test. ceremonials and sacred objects. Symbolism was also naturally characteristic of the Church of the Middle Ages, which undertook to carry home to the eyes, minds, and hearts of the people spiritual truths through external symbols. The origin of some of these it is now difficult to discover. Many naturally suggest the correlative truth to the mind; others make the suggestion through historical or scriptural association. The following is a partial list of some of the principal symbols in use in the Christian churches, for a fuller account of which the reader is referred to Clements [Mrs.], Handbook of Legendary and Mythological Art. The glory, aureole, and nimbus all represent light or lightness, and are symbols of sanctity. The nimbus surrounds the head; the aureole the body; the glory unites the two. The nimbus attaches in Roman Catholic art to all saints; the aureole and glory only to the persons of the Godhead and to the Virgin Mary. The fish is an emblem of Christ. (See Ichthys).
The lamb is a common symbol of Christ. It derives its significance from the fact that it was one of the chief sacrifices of the Jewish Temple, and from the words of John the Baptist, "Behold the lamb of God, which taketh away the sin of the world" ( John 1:29). The lamb is often represented in art bearing a cross. The lion is another symbol of Christ, who in Scripture is called "the Lion of the tribe of Judah" ( Revelation 5:5). The pelican, which is said to bare open her breast to feed her young with blood, is an emblem of redemption. The dove is a symbol of the Holy
Spirit ( Matthew 3:16) issuing from the mouth of the dying, it is an emblem of the soul. The olive-branch is an emblem of peace ( Genesis 8:11); the palm, of martyrdom ( Revelation 7:9). The lily represents chastity; the lamp, piety ( Matthew 25:1-12); fire, zeal or the sufferings of martyrdom; the flaming heart, fervent piety and spiritual love; the peacock, immortality; the crow, victory on women, it signifies the bride of Christ. The sword, axe, lance, and club indicate martyrdom; the skull and scourge, penance; the chalice, faith; the ship, the Christian Church; the anchor, faith ( Hebrews 6:19). Each color also has a symbolic meaning in art, for which (See Color).
In Roman Catholic art, also, each apostle has his own symbol, as follows: Peter, the keys, or a fish; Andrew, the transverse cross which bears his name; James the Greater, the pilgrim's staff; John, the eagle, or the chalice with the serpent; Thomas, a builder's rule; James the Less, a club; Philip, a small cross on a staff, or crosier surmounted by a cross; Bartholomew, a knife; Matthew, a purse; Simon, a saw; Thaddeus, a halberd or lance; Matthias, a lance. The various monastic orders have also each its own symbol. See Jameson and Eastlake, History of Our Lord as Exemplified in Works of Art (Lond. 1864,2 vols.); Didron, Christian Iconography, or History of Christian Art in the Middle Ages (ibid. 1851, ed. Bohn).
The Nuttall Encyclopedia 
Been divided into two kinds, symbolism of colour and symbolism of form. Of colours,
ypifies grief and death;
ope, love of divine works, divine contemplation, piety, sincerity;
ower, Christian prudence, love of good works, serene conscience;
lory and power;
aith, immortality, resurrection, gladness;
artyrdom for faith, charity, divine love;
ervour and glory;
hastity and purity;
urity, temperance, innocence, chastity, and faith in God. Instances of form:
eath or martyrdom; the
urity. Of stones, moreover, the