tick: English now has no fewer than four distinct words tick in general use. The oldest, tick ‘mite’ [OE], comes from a prehistoric West Germanic *tik-, which may be related to Armenian tiz ‘bug’. Tick ‘sound of a clock, mark of correctness, etc’ [13] originally meant broadly ‘light touch, tap’; its modern uses are secondary and comparatively recent developments (‘sound of a clock’ appears to have evolved in the 16th century, and ‘mark of correctness’ did not emerge until the 19th century). Tickle [14] is probably a derivative. Tick ‘mattress case’ [15] was borrowed from Middle Dutch tēke, which went back via Latin thēca to Greek thékē ‘cover, case’.
And tick ‘credit’ [17] (as in on tick) is short for ticket. => tickle; ticket
