A graduate securing second degree ultimately is simple creature (6)
I believe the answer is:
amoeba
'simple creature' is the definition.
(I've seen this before)
'a graduate securing second degree ultimately' is the wordplay.
'graduate' becomes 'ba'.
'securing' means one lot of letters goes inside another.
'second' becomes 'mo' (both are short periods of time).
'ultimately' indicates one should take the final letters.
The last letter of 'degree' is 'e'.
'a'+'ba'='aba'
'mo'+'e'='moe'
'aba' going around 'moe' is 'AMOEBA'.
'is' acts as a link.
(Other definitions for amoeba that I've seen before include "Unicellular form" , "insignificant creature" , "very simple life-form" , "Simple life form" , "O, Mam, be a one-celled animal" .)