Half life is close to being absolutely straight (6)
I believe the answer is:
linear
'absolutely straight' is the definition.
'linear' can be an answer for 'straight' (I've seen this before). I'm not certain of the 'absolutely' bit.
'half life is close to' is the wordplay.
'half life' becomes 'li' (half of word 'life').
'is close to' becomes 'near' (close to means nearby).
'li'+'near'='LINEAR'
'being' is the link.
Can you help me to learn more?
(Other definitions for linear that I've seen before include "Consisting of lines" , "In a straight line" , "adopting common narrative style" , "Like some ancient scripts" , "Involving one dimension only" .)