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Vine's Expository Dictionary of NT Words [1]

1: Χαρά (Strong'S #5479 — Noun Feminine — chara — khar-ah' )

"joy, delight" (akin to A, No. 1 above), is rendered "gladness" in the AV of  Mark 4:16;  Acts 12:14;  Philippians 2:29 (RV "joy," as elsewhere in both versions). See Joy.

2: Ἀγαλλίασις (Strong'S #20 — Noun Feminine — agalliasis — ag-al-lee'-as-is )

"exultation, exuberant joy" (akin to A, No. 2), is translated "gladness" in  Luke 1:14;  Acts 2:6;  Hebrews 1:9; "joy" in  Luke 1:44; "exceeding joy" in  Jude 1:24 . It indicates a more exultant "joy" than No. 1. In the Sept. this word is found chiefly in the Psalms, where it denotes "joy" in God's redemptive work, e.g.,  Psalm 30:5;  42:4;  45:7,15 . See Joy.

3: Εὐφροσύνη (Strong'S #2167 — Noun Feminine — euphrosune — yoo-fros-oo'-nay )

"good cheer, joy, mirth, gladness of heart" (akin to A, No. 3), from eu, "well," and phren, "the mind," is rendered "gladness" in  Acts 2:28 , RV (AV, "joy") and  Acts 14:17 . See Joy.

King James Dictionary [2]

GLAD'NESS, n. See Glad. Joy, or a moderate degree of joy and exhilaration pleasure of mind cheerfulness.

They--did eat their meat with gladness and singleness of heart.  Acts 2

Gladness is rarely or never equivalent to mirth, merriment, gayety and triumph, and it usually expresses less than delight. It sometimes expresses great joy.  Esther 8.9 .