Hello there. 
I would like to ask some pali experts about phrase “passambhayaṁ” which is used in anapana-sati sutta:
‘passambhayaṁ kāyasaṅkhāraṁ assasissāmī’ti sikkhati, ‘passambhayaṁ kāyasaṅkhāraṁ passasissāmī’ti sikkhati.
They practice like this: ‘I’ll breathe in stilling the physical process.’ They practice like this: ‘I’ll breathe out stilling the physical process.’
All translators translate it as more or less tranquilasing/stilling. Suttacentral.net dictrionary says:
passa
masculine & neuter
- side; flank
bhaya
neuter
- fear; fright
And another sutta about breath meditation, AN4.38 says:
Kathañca, bhikkhave, bhikkhu passaddhakāyasaṅkhāro hoti?
And how has a mendicant stilled the physical process?
I wonder, why in MN118 it is passambhayaṁ and in AN4.38 passaddhakāyasaṅkhāro? Why in one it is “passa” and in the other “passaddha”, do they mean the same thing? I ask because passaddhi is much more popular term in general as “tranquility”. I wonder how this “passambhayaṁ” means tranquility. I wonder how word meaning “fear” got there, or perhaps it is some problem with suttacentral dictrionary. If anyone knows, please share.
Sorry if this is silly question. 