Donec denotes the relationship between two actions, at the same time e.g.
"donec, infecta pace, armis desilirent" giving ""while", with peace having been broken off, they came to strive with arms";
"...et non cognoscebat eam, donec peperit filium, et vocavit nomen eius Iusum." giving "...and he did not know (have carnal-knowledge of) her "until" she had given birth to a son, and the name of him she called Jesus." Hence, or otherwise: "He did not have sexual relations with her for "as-long-as" she was pregnant."
Apologies for sparsity, earlier; didn´t want to claim other´´s work as own. The Wiki entry has required some embellishment, however.
With problems like this, type in the word, nothing else, a Wiki-option will appear. If the net cannot identify the word as Latin, it´´s too similar to its English descendant, then add "Latin," followed by the word.