pensing.

pensive.

Origin:
1325–75; < French (feminine); replacing Middle English pensif <

< Middle French (masculine), derivative of penser to think <

< Latin pēnsāre  to weigh, consider, derivative of pēnsus,  

past participle of pendere.

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years ago.

this question would be asked of me:

why are you so quiet?

my reply:

i am pensing.

this word is not in the dictionary.
however: 

it more than adequately defines

why

at times

i am quiet:

i am pensing.

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