Fish in whipped cream served in temporary homes, lesser building units? (5,8)
I believe the answer is:
trace elements
'lesser building units?' is the definition.
(everything is built from elements)
'fish in whipped cream served in temporary homes' is the wordplay.
'fish' becomes 'eel' (eel is a kind of fish).
'in' means one lot of letters goes inside another.
'whipped' indicates anagramming the letters.
'served in' means one lot of letters goes inside another.
'temporary homes' becomes 'tents'.
'cream' anagrammed gives 'racem'.
'eel' going within 'racem' is 'raceelem'.
'raceelem' going inside 'tents' is 'TRACE ELEMENTS'.
(Other definitions for trace elements that I've seen before include "Chemicals found in minimal amounts" , "Essentials to life that occur in very small amounts" .)