From BiblePortal Wikipedia

Vine's Expository Dictionary of NT Words [1]

1: Ἀκατάλυτος (Strong'S #179 — Adjective — akatalutos — ak-at-al'-oo-tos )

denotes indissoluble (from a, negative, kata, "down," luo, "to loose"),  Hebrews 7:16 , "endless;" see the Rv , marg., i.e., a life which makes its possessor the holder of His priestly office for evermore.

2: Ἀπέραντος (Strong'S #562 — Adjective — aperantos — ap-er'-an-tos )

from a, negative and peraino, "to complete, finish," signifies "interminable, endless;" it is said of genealogies,  1—Timothy 1:4 . In the Sept.,  Job 36:26 .

Webster's Dictionary [2]

(1): ( a.) Without profitable end; fruitless; unsatisfying.

(2): ( a.) Void of design; objectless; as, an endless pursuit.

(3): ( a.) Without end; having no end or conclusion; perpetual; interminable; - applied to length, and to duration; as, an endless line; endless time; endless bliss; endless praise; endless clamor.

(4): ( a.) Infinite; excessive; unlimited.

King James Dictionary [3]

END'LESS, a. See End. Without end having no end or conclusion applied to length, and to duration as an endless line endless progression endless duration endless bliss.

1. Perpetual incessant continual as endless praise endless clamor.

International Standard Bible Encyclopedia [4]

end´les ( ἀκατάλυτος , akatálutos ( Hebrews 7:16 , ἀπέραντος , apérantos ( 1 Timothy 1:4 )): This English word occurs twice in the New Testament, and is there represented by the two Greek words above noted.

(1) In  Hebrews 7:16 Jesus is said to be a priest "after the power of an endless life." The word means literally, as in the Revised Version, margin, "indissoluble." It is not simply that Christ's priesthood was eternal. The priesthood was based upon His possession, by nature, of a life which in time and eternity death could not touch. This distinguished Him essentially from priests under the law.

(2) In  1 Timothy 1:4 , Paul warns Timothy against giving heed in his ministry to "fables ( múthoi ) and endless (limitless) genealogies." The allusion seems to be to the series of emanations (aeons) in Gnostic speculation, to which no limit could be set.

Distinct from the above are the words denoting "everlasting," "eternal," which see.