“Pecan” is from an Algonquian word variously referring to pecans, walnuts and hickory nuts. There are many variant pronunciations, some regional and others not. The most common American pronunciation is /pɪˈkɑːn/; the most common British one is /pɪˈkæn/. There is little agreement in the United States, even regionally, as to the “correct” pronunciation.
The pecan tree is a large deciduous tree, growing to 20–40 m (66–131 ft) in height, rarely to 44 m (144 ft). It typically has a spread of 12–23 m (39–75 ft) with a trunk up to 2 m (6.6 ft) diameter. A 10-year-old sapling grown in optimal conditions will stand about 5 m (16 ft) tall. The leaves are alternate, 30–45 cm (12–18 in) long, and pinnate with 9–17 leaflets, each leaflet 5–12 cm (2.0–4.7 in) long and 2–6 cm (0.79–2.36 in) broad.
A pecan, like the fruit of all other members of the hickory genus, is not truly a nut, but is technically a drupe, a fruit with a single stone or pit, surrounded by a husk. The husks are produced from the exocarp tissue of the flower, while the part known as the nut develops from the endocarp and contains the seed. The husk itself is aeneous, that is, brassy greenish-gold in color, oval to oblong in shape, 2.6–6 cm (1.0–2.4 in) long and 1.5–3 cm (0.59–1.18 in) broad. The outer husk is 3–4 mm (0.12–0.16 in) thick, starts out green and turns brown at maturity, at which time it splits off in four sections to release the thin-shelled seed.