Aft

google

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early 17th century: probably from obsolete baft (see abaft), influenced by Low German and Dutch achter ‘abaft, after’.

wiktionary

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From Old English æftan(“behind”); originally superlative of of(“off”). See after.

Clipping of  afternoon. 

etymonline

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aft (adv.)

Old English æftan "from behind, behind, farthest back," superlative of Old English æf, af, of "away, away from, off" (from PIE root *apo- "off, away"). Cognate with Old Frisian eft "later, afterwards; as well," Old Norse eft "after," Middle Dutch echter, efter "later, again," Gothic afta "behind, past." The Germanic superlative suffix *-ta corresponds to PIE *-to (compare Greek prōtos "first," superlative of pro "before"). The word is now purely nautical, "in, near, or toward the stern of a ship."