To suffer keenly

writhe (intransitive)
3: to suffer keenly

1 keen
1

a : having a fine edge or point : http://www.merriam-webster.com/dictionary/sharp b : affecting one as if by cutting <keen sarcasm> c : pungent to the sense <a keen scent>

2

a (1) : showing a quick and ardent responsiveness : http://www.merriam-webster.com/dictionary/enthusiastic <a keen swimmer> (2) : http://www.merriam-webster.com/dictionary/eager <was keen to begin> b of emotion or feeling : http://www.merriam-webster.com/dictionary/intense <the keen delight in the chase — F. W. Maitland>

3

a : intellectually alert : having or characteristic of a quick penetrating mind <a keen student> <a keen awareness of the problem>; also : shrewdly astute b : sharply contested <keen debate> c : extremely sensitive in perception <keen eyes>

4

: http://www.merriam-webster.com/dictionary/wonderful, http://www.merriam-webster.com/dictionary/excellent

[M-W's Col. Dic.]

Which definition of "keen" is more fitting in "to suffer keenly", is it 2b? Please let me know.