vi·tal -adjective

1. of or pertaining to life: vital process
2. being the seat or source of life: the vital organs
3. necessary to life and continuation of life: vital fluids
4. necessary to the existence, continuance, or well being of something; essential: vital for a healthy society
5. affecting the existence, weel-being, truth, of something: a vital error
6. of critical importance: vital decisions
7. necessary for the success or continued existence of something; extremely important; essential

synomyms: basic, crucial, decisive, important, indispensable, key, meaningful, necessary, needed, required, significant, urgent

di·gres·sion -noun

1. a message that departs from the main subject; an exploration of a different or unrelated concern: excurses, divagation, parenthesis
2. a turning aside (of your course or attention or concern): diversion, deviation, defelction, deflexion, divigation
3. wandering from the main path of a journey

synonyms: aside, departure, difference, divergence, diversion, episode, excursion, rambling, variation, wandering