get cracking vs begin

get cracking and begin both are verbs.

Word	Noun	Adjective	Verb	Adverb
get cracking	No	No	Yes	No
begin	No	No	Yes	No

As verbs, begin is a hypernym of get cracking; that is, begin is a word with a broader meaning than get cracking:

Other hypernyms of get cracking include commence, get, get down, set about, set out, start, start out.

get cracking (verb)	begin (verb)
start to be active	take the first step or steps in carrying out an action
	set in motion, cause to start
	begin to speak or say
	begin to speak, understand, read, and write a language
	achieve or accomplish in the least degree, usually used in the negative
	begin an event that is implied and limited by the nature or inherent function of the direct object
	have a beginning, in a temporal, spatial, or evaluative sense
	be the first item or point, constitute the beginning or start, come first in a series
	have a beginning characterized in some specified way
	have a beginning, of a temporal event