Lay hold of a fly in the ointment (5)
I believe the answer is:
catch
This clue might be a double definition.
'lay hold' is the first definition.
'catch' can be an answer for 'hold' (thesaurus). I'm not certain of the 'lay' bit.
'fly in the ointment' is the second definition.
(I've seen this in another clue)
'of a' acts as a link.
Can you help me to learn more?
(Other definitions for catch that I've seen before include "Seize; start burning" , "(To) snare, net" , "Concealed difficulty" , "Trap (a batsman?)" , "Fastener on door or window" .)