A lieutenant: he meets a lady (6)
I believe the answer is:
althea
'lady' is the definition.
'a lieutenant he meets a' is the wordplay.
'lieutenant' becomes 'lt' (abbreviation for lieutenant).
'meets' means one lot of letters go next to another.
'a'+'lt'+'he'+'a'='ALTHEA'
(Other definitions for althea that I've seen before include "Girl" , "wholesome woman" , "female" .)