名词 second hand:
an intermediate person; used in the phrase `at second hand'
hand marking seconds on a timepiece
derived from what is primary or original; not firsthand
previously used or owned by another
from a source of previously owned goods
by indirect means
secondness second second national land investigation second order elasto-optic effect second degree price discrimination second-order necessary condition second generation current conveyor second-order nonlinear filtering Second School of Clinical Medicine second language acquisition theory Second of two possible upgrades. second-order difference equation