Crossword Genius

Building laboratory's extremities in a playful way (6)

Ross

I believe the answer is:

archly

I'm a little stuck... Click here to teach me more about this clue!

'in a playful way' is the definition.
I can't judge whether this defines the answer.

'building laboratory's extremities' is the wordplay.
'building' becomes 'arch'.
'laboratory's extremities' becomes 'ly' (I am not sure about this - if you are sure you should believe this answer much more).
'arch'+'ly'='ARCHLY'

Can you help me to learn more?

(Other definitions for archly that I've seen before include "In roguish manner" , "In a sly way" , "In a sly manner" .)

I've seen this clue in The Daily Express.
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