Minute arachnid (4)
This clue is a double definition.
'minute' is the first definition.
(I've seen this before)
'arachnid' is the second definition.
(tick is a kind of arachnid)
(Other definitions for tick that I've seen before include "Make noise like old clock" , "sucker" , "Check mark" , "Small parasitic arachnid" , "Clock's sound" .)
'minute arachnid' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for mite that I've seen before include "Minute arachnid" , "The widow's small offering" , "The Biblical widow's offering" , "Little chap" , "Tiny contribution, child" .)