Bronch/o and bronchi/o mean bronchus. The word that means dilation or expansion of the bronchus is:

Bronchiectasis

Explanation:

Bronchiectasis literally means the state of expansion of the bronchial tubes in a way that is different from what its usually used to be. This abnormality usually occurs due to the outcome of preceding lung disease (chronic infections) e. g allergic bronchopulmonary aspergillosis or cystic fibrosis.

Blockage of the bronchi can result from tumour, foreign objects (e. g., hard objects such as coin, food) etc. This blockage may lead to amassing and static inactivation of secretions and infections in the bronchial walls.

Chronic infections cause continued inflammation of the bronchial walls, hence the elastic and muscle fibres tend to deteriorate, and this deterioration allows the dilatation of the bronchi.