Openly showed sign of boredom (6)
I believe the answer is:
yawned
'openly showed' is the definition.
Although both the answer and definition are past participle verbs, I can't understand how one could define the other.
'sign of boredom' is the wordplay.
'sign' becomes 'yawn' (I have seen 'Sign of tiredness ' mean 'yawn' so perhaps 'sign' could also mean 'yawn').
'of boredom' becomes 'ed' (I can't explain this - if you can you should give a lot more credence to this answer).
'yawn'+'ed'='YAWNED'
Can you help me to learn more?
(Other definitions for yawned that I've seen before include "Showed tiredness or boredom" , "Breathed deeply with mouth wide open" , "Gave mute evidence of boredom" , "Gaped, with tiredness?" , "Demonstrated tiredness (or boredom!)" .)