Step 1: Understanding the Concept:
This question is based on the rule of 'Jashatva Sandhi' under Vyanjana Sandhi. The formula for Jashatva Sandhi is 'Jhalām Jaśo'n'te'.
Step 2: Key Formula or Approach:
According to the rule of Jashatva Sandhi, if the first letter of a class (क्, च्, ट्, त्, प्) is followed by a vowel or the third, fourth letter of any class or य, र, ल, व, ह, then the first letter of the class changes to the third letter of its own class (ग्, ज्, ड्, द्, ब्).
\[ त् + (Third/Fourth letter of a class) \rightarrow द् \]
Step 3: Detailed Explanation:
The given words are 'उत्' and 'देशः'.
The last letter of the first word is 'त्' (the first letter of the 'त' class).
The first letter of the second word is 'द' (the third letter of the 'त' class).
According to the rule, when 'द' follows 'त्', 'त्' will change to 'द्', the third letter of its own class.
\[ उत् + देशः \rightarrow उद् + देशः \rightarrow उद्देशः \]
Step 4: Final Answer:
Therefore, combining 'उत्' and 'देशः' forms the word 'उद्देशः'.