A very large swift with broad wings pinched at the base, a protruding front, and a bulky rear. Short tail has well-defined spines that can be seen even in fast flight. It has blackish-brown upperparts with a pale-brown saddle, often difficult to make out; the underparts from the throat to the lower breast are dark brown, ending in a well-demarcated deep “V” that contrasts strongly with the white belly, vent, and undertail.