Trick's beginning with bottom card of winning suit (5)
I believe the answer is:
trump
'card of winning suit' is the definition.
'trump' can be an answer for 'card' (e.g. in bridge or whist). I'm unsure of the 'of winning suit' bit.
'trick's beginning with bottom' is the wordplay.
'beginning' indicates taking the first letters.
'with' says to put letters next to each other.
'bottom' becomes 'rump' (rump can informally mean someone's bottom).
The initial letter of 'tricks' is 't'.
't'+'rump'='TRUMP'
Can you help me to learn more?
(Other definitions for trump that I've seen before include "reliable person" , "High-ranking card" , "A playing card given added value in some games" , "Outdo (with a card?)" , "Powerful playing card" .)