Conjuring trick

I woke and found it on my lips –
Ineffable : a word to conjure with;
A word replete with gravity and grace;
A Sunday word – I sang it in a hymn
Describing Godly might or mystery, perhaps.

Grammatical investigation now:
The suffixes are shed to left and right
And I am left at last with lonely eff.
The whole charade has been a rotten con
To lead me up the effing garden path!