Perhaps man arriving without jacket concealed trousers (7)
I believe the answer is:
hominid
'perhaps man' is the definition.
'hominid' can be an answer for 'man' (I have seen 'Old man' mean 'hominid' so perhaps 'man' could also mean 'hominid'). I'm not certain of the 'perhaps' bit.
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for hominid that I've seen before include "Man's cousin" , "Member of zoological family of humans and ancestors" , "Man or manlike creature" , "Old man" , "Man, including fossil types" .)