Gradus ad Parnassum n.

Proto-Indo-European root meaning "to walk, go." 

It forms all or part of: aggress; aggression; aggressive; centigrade; congress; degrade; degree; degression; digress; digression; egress; gradation; grade; gradual; graduate; grallatorial; gravigrade; ingredient; ingress; plantigrade; progress; progression; regress; regression; retrograde; retrogress; tardigrade; transgress; transgression.

It is the hypothetical source of/evidence for its existence is provided by: Latin gradus "a step, a pace, gait," figuratively "a step toward something, a degree of something rising by stages;" gradi "to walk, step, go;" Lithuanian gridiju, gridyti "to go, wander;" Old Church Slavonic gredo "to come;" Old Irish in-greinn "he pursues."  

"the abiding place of poetry, the home of the poets," late 14c., Parnaso, from Italian, from Latin Parnassus, from Greek Parnassos, Parnasos, mountain chain in central Greece, sacred to Apollo and the Muses, thus symbolic of poetry. Ancient sources say the older name was Larnassos; Beekes hints at a Pre-Greek origin. Related: Parnassian.

Various kinds of literary fame seem destined to various measures of duration. Some spread into exuberance with a very speedy growth, but soon wither and decay; some rise more slowly, but last long. Parnassus has its flowers of transient fragrance, as well as its oaks of towering height, and its laurels of eternal verdure. [Samuel Johnson, "The Rambler," March 23, 1751]