I am having trouble in figuring it out why there is a difference between their meaning as i think that the root "content" is shared by both the words content + ious ; content + ment where contentment means a sense of satisfaction and contentious is being argumentative - newbie (please correct me if i am wrong)
The similarity obscures the different etymologies.
Content, taken over exactly from Old French, ultimately comes from Latin contentus, "contained, satisfied," past participle of continere. Related words are contents (that which is contained) or incontinent (inability to contain urination).
The two words have nothing to do with each other etymologically, as they derive from two different Latin verbs.
The OED gives the following for 'contentious':
Etymology: < French contentieux < Latin contentiōsus given to contention, quarrelsome:
a. Of persons or their dispositions: Given to contention; prone to strife or dispute; quarrelsome.
1533 J. Frith Bk. answeringe Mores Let. sig. Oivv That you accept this worke with..no contencious harte. 1611 Bible (King James) Prov. xxi. 19 It is better to dwell in the wildernesse, then with a contentious and an angry woman.
The OED entry for 'contentment' is :
Etymology: < French contentement (late 16th cent. in Littré), < contenter to content v.:
a. The action of satisfying; the process of being satisfied; satisfaction. arch.
▸c1475 in Coll. Ordinances Royal Househ. (Harl. 642) (1790) 22 For the contentement of his household royal and creditors thereof. 1576 A. Fleming tr. Cicero in Panoplie Epist. 35 The Victor..must doe many thinges to the expectation and contentment of them, by whose helpe he obteined the victorie.
The words seem to have come straight into English from the French. 'Contentious' appears first as 'contencious' in 1533, but changes to 'contentious' in the 1611 Authorised Version of the bible.
And 'contentment' first appears in its French form 'contentement' in 1475.
I would say that the origin of the suffixes and their disparate meanings is a matter of the French etymology rather than any English manipulation.