The antonyms for the word "casting loose" include "attaching," "fastening," "tying," "securing," "binding," and "connecting." These are all actions that involve fixing something in a stable or permanent position, in contrast to casting loose which means to let go or free. While casting loose may be appropriate for some situations, such as releasing a boat or animal into the wild, attaching or securing is necessary for other tasks, such as anchoring a boat or tying a package. The right antonym depends on the context and the desired outcome of the action.