Thy mercy
checed (kheh'-sed)
kindness; by implication (towards God) piety: rarely (by opposition) reproof, or (subject.) beauty
O LORD
Yhovah (yeh-ho-vaw')
(the) self-Existent or Eternal; Jehovah, Jewish national name of God -- Jehovah, the Lord.
is in the heavens
shamayim (shaw-mah'-yim)
air, astrologer, heaven(-s).
and thy faithfulness
'emuwnah (em-oo-naw')
literally firmness; figuratively security; morally fidelity -- faith(-ful, -ly, -ness, (man), set office, stability, steady, truly, truth, verily.
reacheth unto the clouds
shachaq (shakh'-ak)
a powder (as beaten small): by analogy, a thin vapor; by extension, the firmament -- cloud, small dust, heaven, sky.