Pencilled in typically refers to tentative plans or commitments. Antonyms for pencilled in could include any words that signify a definite or final arrangement. Some examples could be arranged, confirmed, scheduled, designated, ordained, or fixed. These words would indicate a firm and agreed-upon plan or commitment, rather than one that is subject to change or uncertainty. By contrast, language that is more tentative would include words like tentative, conditional, hypothetical, or provisional. It is important to choose the right words to express our intentions accurately and effectively, so our audience can understand the level of certainty behind our plans or commitments.