The Sierra Nahuat have cognatic descent and do not form descent groups. Kinship terminplogy in the first ascending generation is Eskimo; father ( taht ) and mother ( nan ) are differentiated from father's and mother's brother ( tahitzin ) and father's and mother's sister ( āhui ). Terms in Ego's generation are either Hawaiian, with one term ( icnīuh ) applied to all cognatic blood kin in the speaker's generation. The Nahua of the sixteenth century used different terms for siblings, depending on the gender of the speaker, and terminologically distinguished siblings by their gender and their age relative to the speaker. Male and female Sierra Nahuat speakers of today generally use the same sibling terms and specify gender and relative age by adding qualifying words to the general term for sibling/cousin (icnīuh). Nocnīuh tācat ("my sibling/cousin who is a man") and nocnīuh cihuāt ("my sibling/cousin who is a woman") denote gender. Nocnīuh tayacāna ("my sibling/cousin who is ahead") and nocnīuh tacuitapan ("my sibling/cousin who is behind") specify relative age. Many speakers use the abbreviated terms tayacānqueh ("he who is ahead") for oldest or firstborn sibling and taxocōyot ("spoiled one") for youngest or lastborn sibling. Tayacānqueh sometimes refers to the eldest brother who succeeds the father as head of the household. Men and women still use different affinal terms for spouse's siblings.