1 haphazard, chance, fortuitous, serendipitous, aleatory, arbitrary, casual, stray, occasional, indefinite, indiscriminate, non-specific, unspecific, unspecified, unordered, unorganized, undirected, unpremeditated, unplanned, accidental, uncalculated, unsystematic, adventitious, incidental, hit-or-miss:
He used a computer program to generate random numbers. A random selection of slips was drawn from the drum and Madelaine's name was on one of them
2 at random. randomly, haphazardly, fortuitously, by chance, serendipitously, arbitrarily, casually, occasionally, (every) now and then, (every) once in a while, irregularly, indefinitely, erratically, indiscriminately, unsystematically, adventitiously, incidentally, unpremeditatedly:
They picked names from a hat at random. They drove up and down the road, firing at random.