exigent

1. Requiring immediate action or remedy. See synonyms at urgent.
2. Requiring much effort or expense; demanding.

[Latin exigēns, exigent-, present participle of exigere, to demand. See exact.]

adjective

1. Compelling immediate attention: burning, crying, dire, emergent, imperative, instant, pressing, urgent. See big/small/amount.
2. Requiring great or extreme bodily, mental, or spiritual strength: arduous, backbreaking, burdensome, demanding, difficult, effortful, exacting, formidable, hard, heavy, laborious, onerous, oppressive, rigorous, rough, severe, taxing, tough, trying, weighty. See heavy/light.

Definition: difficult, taxing
Antonyms: easy, facile, unpressured

adj

Definition: urgent, pressing
Antonyms: ordinary, unpressured, usual

The adjective has 2 meanings:

Meaning #1: demanding attention
  Synonyms: clamant, crying, insistent, instant

Meaning #2: requiring precise accuracy
  Synonym: exacting