Informally intend to secure a monitor (6)
I believe the answer is:
goanna
'monitor' is the definition.
(type of monitor lizard)
'informally intend to secure a' is the wordplay.
'informally intend' becomes 'gonna' ('I'm gonna do it').
'to secure' means one lot of letters goes inside another (inserted letters are secured inside).
'gonna' enclosing 'a' is 'GOANNA'.
(Other definitions for goanna that I've seen before include "Australian resident" , "large lizard" .)