Had he a strange urge, for a bit of a lark, to join the army? (7)
I believe the answer is:
regular
'the army?' is the definition.
(synonyms)
'had he a strange urge for a bit of a lark to join' is the wordplay.
'had he' becomes 'r' (I can't justify this - if you can you should believe this answer much more).
'a strange' indicates anagramming the letters.
'for' is a charade indicator (letters next to each other) (I've seen this in other clues).
'bit of' indicates taking the first letters.
'to join' is a charade indicator (letters next to each other).
The initial letter of 'lark' is 'l'.
'a'+'l'='al'
'urge' after 'al' is 'alurge'.
'alurge' with letters rearranged gives 'egular'.
'r'+'egular'='REGULAR'
Can you help me to learn more?
(Other definitions for regular that I've seen before include "Normal, steady" , "Recurring at short uniform intervals" , "Occurring at fixed intervals" , "In accordance with a fixed order" , "Recurring in a uniform manner, say pulse" .)